/*-------------------------------------------------------------------------
 *
 * _int_selfuncs.c
 *      Functions for selectivity estimation of intarray operators
 *
 * Portions Copyright (c) 1996-2017, PostgreSQL Global Development Group
 * Portions Copyright (c) 1994, Regents of the University of California
 *
 *
 * IDENTIFICATION
 *      contrib/intarray/_int_selfuncs.c
 *
 *-------------------------------------------------------------------------
 */
#include "postgres.h"
#include "_int.h"

#include "access/htup_details.h"
#include "catalog/pg_operator.h"
#include "catalog/pg_statistic.h"
#include "catalog/pg_type.h"
#include "utils/builtins.h"
#include "utils/selfuncs.h"
#include "utils/syscache.h"
#include "utils/lsyscache.h"
#include "miscadmin.h"

PG_FUNCTION_INFO_V1(_int_overlap_sel);
PG_FUNCTION_INFO_V1(_int_contains_sel);
PG_FUNCTION_INFO_V1(_int_contained_sel);
PG_FUNCTION_INFO_V1(_int_overlap_joinsel);
PG_FUNCTION_INFO_V1(_int_contains_joinsel);
PG_FUNCTION_INFO_V1(_int_contained_joinsel);
PG_FUNCTION_INFO_V1(_int_matchsel);


static Selectivity int_query_opr_selec(ITEM *item, Datum *values, float4 *freqs,
                    int nmncelems, float4 minfreq);
static int    compare_val_int4(const void *a, const void *b);

/*
 * Wrappers around the default array selectivity estimation functions.
 *
 * The default array selectivity operators for the @>, && and @< operators
 * work fine for integer arrays. However, if we tried to just use arraycontsel
 * and arracontjoinsel directly as the cost estimator functions for our
 * operators, they would not work as intended, because they look at the
 * operator's OID. Our operators behave exactly like the built-in anyarray
 * versions, but we must tell the cost estimator functions which built-in
 * operators they correspond to. These wrappers just replace the operator
 * OID with the corresponding built-in operator's OID, and call the built-in
 * function.
 */

Datum
_int_overlap_sel(PG_FUNCTION_ARGS)
{
    PG_RETURN_DATUM(DirectFunctionCall4(arraycontsel,
                                        PG_GETARG_DATUM(0),
                                        ObjectIdGetDatum(OID_ARRAY_OVERLAP_OP),
                                        PG_GETARG_DATUM(2),
                                        PG_GETARG_DATUM(3)));
}

Datum
_int_contains_sel(PG_FUNCTION_ARGS)
{
    PG_RETURN_DATUM(DirectFunctionCall4(arraycontsel,
                                        PG_GETARG_DATUM(0),
                                        ObjectIdGetDatum(OID_ARRAY_CONTAINS_OP),
                                        PG_GETARG_DATUM(2),
                                        PG_GETARG_DATUM(3)));
}

Datum
_int_contained_sel(PG_FUNCTION_ARGS)
{
    PG_RETURN_DATUM(DirectFunctionCall4(arraycontsel,
                                        PG_GETARG_DATUM(0),
                                        ObjectIdGetDatum(OID_ARRAY_CONTAINED_OP),
                                        PG_GETARG_DATUM(2),
                                        PG_GETARG_DATUM(3)));
}

Datum
_int_overlap_joinsel(PG_FUNCTION_ARGS)
{
    PG_RETURN_DATUM(DirectFunctionCall5(arraycontjoinsel,
                                        PG_GETARG_DATUM(0),
                                        ObjectIdGetDatum(OID_ARRAY_OVERLAP_OP),
                                        PG_GETARG_DATUM(2),
                                        PG_GETARG_DATUM(3),
                                        PG_GETARG_DATUM(4)));
}

Datum
_int_contains_joinsel(PG_FUNCTION_ARGS)
{
    PG_RETURN_DATUM(DirectFunctionCall5(arraycontjoinsel,
                                        PG_GETARG_DATUM(0),
                                        ObjectIdGetDatum(OID_ARRAY_CONTAINS_OP),
                                        PG_GETARG_DATUM(2),
                                        PG_GETARG_DATUM(3),
                                        PG_GETARG_DATUM(4)));
}

Datum
_int_contained_joinsel(PG_FUNCTION_ARGS)
{
    PG_RETURN_DATUM(DirectFunctionCall5(arraycontjoinsel,
                                        PG_GETARG_DATUM(0),
                                        ObjectIdGetDatum(OID_ARRAY_CONTAINED_OP),
                                        PG_GETARG_DATUM(2),
                                        PG_GETARG_DATUM(3),
                                        PG_GETARG_DATUM(4)));
}


/*
 * _int_matchsel -- restriction selectivity function for intarray @@ query_int
 */
Datum
_int_matchsel(PG_FUNCTION_ARGS)
{
    PlannerInfo *root = (PlannerInfo *) PG_GETARG_POINTER(0);

    List       *args = (List *) PG_GETARG_POINTER(2);
    int            varRelid = PG_GETARG_INT32(3);
    VariableStatData vardata;
    Node       *other;
    bool        varonleft;
    Selectivity selec;
    QUERYTYPE  *query;
    Datum       *mcelems = NULL;
    float4       *mcefreqs = NULL;
    int            nmcelems = 0;
    float4        minfreq = 0.0;
    float4        nullfrac = 0.0;
    AttStatsSlot sslot;

    /*
     * If expression is not "variable @@ something" or "something @@ variable"
     * then punt and return a default estimate.
     */
    if (!get_restriction_variable(root, args, varRelid,
                                  &vardata, &other, &varonleft))
        PG_RETURN_FLOAT8(DEFAULT_EQ_SEL);

    /*
     * Variable should be int[]. We don't support cases where variable is
     * query_int.
     */
    if (vardata.vartype != INT4ARRAYOID)
        PG_RETURN_FLOAT8(DEFAULT_EQ_SEL);

    /*
     * Can't do anything useful if the something is not a constant, either.
     */
    if (!IsA(other, Const))
    {
        ReleaseVariableStats(vardata);
        PG_RETURN_FLOAT8(DEFAULT_EQ_SEL);
    }

    /*
     * The "@@" operator is strict, so we can cope with NULL right away.
     */
    if (((Const *) other)->constisnull)
    {
        ReleaseVariableStats(vardata);
        PG_RETURN_FLOAT8(0.0);
    }

    /* The caller made sure the const is a query, so get it now */
    query = DatumGetQueryTypeP(((Const *) other)->constvalue);

    /* Empty query matches nothing */
    if (query->size == 0)
    {
        ReleaseVariableStats(vardata);
        return (Selectivity) 0.0;
    }

    /*
     * Get the statistics for the intarray column.
     *
     * We're interested in the Most-Common-Elements list, and the NULL
     * fraction.
     */
    if (HeapTupleIsValid(vardata.statsTuple))
    {
        Form_pg_statistic stats;

        stats = (Form_pg_statistic) GETSTRUCT(vardata.statsTuple);
        nullfrac = stats->stanullfrac;

        /*
         * For an int4 array, the default array type analyze function will
         * collect a Most Common Elements list, which is an array of int4s.
         */
        if (get_attstatsslot(&sslot, vardata.statsTuple,
                             STATISTIC_KIND_MCELEM, InvalidOid,
                             ATTSTATSSLOT_VALUES | ATTSTATSSLOT_NUMBERS))
        {
            Assert(sslot.valuetype == INT4OID);

            /*
             * There should be three more Numbers than Values, because the
             * last three (for intarray) cells are taken for minimal, maximal
             * and nulls frequency. Punt if not.
             */
            if (sslot.nnumbers == sslot.nvalues + 3)
            {
                /* Grab the lowest frequency. */
                minfreq = sslot.numbers[sslot.nnumbers - (sslot.nnumbers - sslot.nvalues)];

                mcelems = sslot.values;
                mcefreqs = sslot.numbers;
                nmcelems = sslot.nvalues;
            }
        }
    }
    else
        memset(&sslot, 0, sizeof(sslot));

    /* Process the logical expression in the query, using the stats */
    selec = int_query_opr_selec(GETQUERY(query) + query->size - 1,
                                mcelems, mcefreqs, nmcelems, minfreq);

    /* MCE stats count only non-null rows, so adjust for null rows. */
    selec *= (1.0 - nullfrac);

    free_attstatsslot(&sslot);
    ReleaseVariableStats(vardata);

    CLAMP_PROBABILITY(selec);

    PG_RETURN_FLOAT8((float8) selec);
}

/*
 * Estimate selectivity of single intquery operator
 */
static Selectivity
int_query_opr_selec(ITEM *item, Datum *mcelems, float4 *mcefreqs,
                    int nmcelems, float4 minfreq)
{
    Selectivity selec;

    /* since this function recurses, it could be driven to stack overflow */
    check_stack_depth();

    if (item->type == VAL)
    {
        Datum       *searchres;

        if (mcelems == NULL)
            return (Selectivity) DEFAULT_EQ_SEL;

        searchres = (Datum *) bsearch(&item->val, mcelems, nmcelems,
                                      sizeof(Datum), compare_val_int4);
        if (searchres)
        {
            /*
             * The element is in MCELEM.  Return precise selectivity (or at
             * least as precise as ANALYZE could find out).
             */
            selec = mcefreqs[searchres - mcelems];
        }
        else
        {
            /*
             * The element is not in MCELEM.  Punt, but assume that the
             * selectivity cannot be more than minfreq / 2.
             */
            selec = Min(DEFAULT_EQ_SEL, minfreq / 2);
        }
    }
    else if (item->type == OPR)
    {
        /* Current query node is an operator */
        Selectivity s1,
                    s2;

        s1 = int_query_opr_selec(item - 1, mcelems, mcefreqs, nmcelems,
                                 minfreq);
        switch (item->val)
        {
            case (int32) '!':
                selec = 1.0 - s1;
                break;

            case (int32) '&':
                s2 = int_query_opr_selec(item + item->left, mcelems, mcefreqs,
                                         nmcelems, minfreq);
                selec = s1 * s2;
                break;

            case (int32) '|':
                s2 = int_query_opr_selec(item + item->left, mcelems, mcefreqs,
                                         nmcelems, minfreq);
                selec = s1 + s2 - s1 * s2;
                break;

            default:
                elog(ERROR, "unrecognized operator: %d", item->val);
                selec = 0;        /* keep compiler quiet */
                break;
        }
    }
    else
    {
        elog(ERROR, "unrecognized int query item type: %u", item->type);
        selec = 0;                /* keep compiler quiet */
    }

    /* Clamp intermediate results to stay sane despite roundoff error */
    CLAMP_PROBABILITY(selec);

    return selec;
}

/*
 * Comparison function for binary search in mcelem array.
 */
static int
compare_val_int4(const void *a, const void *b)
{
    int32        key = *(int32 *) a;
    const Datum *t = (const Datum *) b;

    return key - DatumGetInt32(*t);
}
